[aerohead]

We'd really need a dimensioned, technical drawing of the truck, with everything shown in 'true length', which we could measure and scale from.
The airdam, when fully deployed, is likely increasing frontal area, and we'd need that new value, along with the actual drag force, to reverse-engineer it's Cd, at this increased frontal area, normalized to 'Standard Air'.
Vman455 shared an SAE Paper from Ford a few years back, where they were reporting on 'fixed' airdam research with a F-150 also. The grad students, or PhD candidates who conducted the research, also failed to communicate the change in the truck's frontal area as they increased 'depth' from the original dimension.